1. Field of the Invention
The present invention relates to a fabrication method for a liquid crystal panel, and more particular to an exposure mask for fabricating a color filter, and a method for integrating the color filter into a thin film transistor array substrate (Color filter on array, COA).
2. Description of Related Art
The liquid crystal display (LCD) is an ultra-thin and flat display device, which consists of a number of color or monochrome pixels, and placed in front of a light source or a reflection surface. The power consumption of the LCD is very low, and the LCD has features of high-quality, small size, and light weight, such that everyone likes the LCD, and the LCD becomes the mainstream display. Currently, the LCD is mainly the thin-film transistor (TFT) LCD.
The reason that the TFT-LCD can develop rapidly is based on the amorphous silicon platform (of course, a small part of the product uses polysilicon), therefore, the TFT-LCD is cheap, simple in process, and more uniform, so that there are 55 inches, 65 inches large-sized products. When the size of the LCD become larger, the impedance of the circuit is increased, therefore, it is necessary to use a bigger, thicker or better conductivity metal line. The thickness cannot be increased infinitely, and the best material for conductivity is metal silver and copper. The better and useful conductive material cannot be found in a long time. As a result, the only way is increasing the line width; however, the aperture ratio of the TFT-LCD would reduce by this way.
For the shortcoming of the low aperture ratio of the TFT-LCD, there are many solutions to solve this shortcoming from technical point of view, such as using a metal line with lower impedance, using more challenging design, or using some of the new display modes. One of the ways is to integrate a color filter into the TFT array substrate (called Color filter on array, COA). As shown in FIG. 1, which shows a liquid crystal panel using the COA technology, and the liquid crystal panel includes an upper glass substrate 10, a lower glass substrate 20 and a liquid crystal layer 30 disposed between the upper glass substrate 10 and the lower glass substrate 20.
A side of the lower glass substrate 20 close to the liquid crystal layer 30 is provided with a plurality of TFTs 201, each TFT 201 connects to a pixel electrode 205 correspondingly. Usually, a transparent passivation layer is disposed on the pixel electrode 205. Because of using the COA technology, a color filter 203 is disposed between the TFT 201 and the pixel electrode 205. The color filter 203 includes a red color filter unit 203R, a green color filter unit 203G, and a blue color filter unit 203B. Wherein, each pixel electrode 205 corresponds to one red color filter unit 203R, one green color filter 203G, or one blue color filter unit cell 203B. Wherein, between the TFT 201 and the color filter 203, a first insulation protection layer 202 is provided for isolation. Between the color filter 203 and the pixel electrode 205, a second insulation protection layer 204 is provided for isolation. A side of the upper glass substrate 10 close to the liquid crystal layer 30 is provided with an array of black matrix 101. Each black matrix 101 corresponds to an adjacent region of two of the red color filter unit 203R, the green filter 203G, and the blue color filter unit 203B to prevent light leakage. An ITO common electrode 102 is covered on the array of black matrix 101. Comparing to conventional liquid crystal panel, the problem of misaligning of color filter unit and pixel electrode does not exist so as to increase the aperture ratio of the liquid crystal panel.
However, in this configuration of the liquid crystal panel, the color filter 203 is fabricated on the TFT 201, in the fabrication process of the liquid crystal panel, the color filter 203 is fabricated by photolithography process, and the color filter units 203R, 203G, and 203B with three different colors are fabricated sequentially by three photolithography processes. In order to prevent light leakage, the adjacent two of the color filter units 203R, 203G, and 203B have to connect closely. As shown in FIG. 2, using the red color filter unit 203R and the green color filter unit 203G as an example. A connection portion of the red color filter unit 203R and the green color filter unit 203G is connected closely, and edge portions of the two color filter units are overlapped. At the overlapped portion, there exists a convex portion. The convex portion is called an angle level difference, and an overlapped height is h. If the angle level difference is too large, it will causes many problems such as light leakage between two color filter units. Therefore, in the fabrication process of the color filter, controlling the height h of the angle level difference is required.